Topic: NEWB requesting advice/help for upcoming concert

[landshark]

Hey guys -

Here's one way to think about the whole battery box / preamp thing.

Battery box and mic power:

When you tape, you use a microphone to convert sound energy into electrical waves.  The mics you're using do this by creating a charged field that vibrates from the sound waves.  The lower the frequency, the larger (and more powerful) the sound wave.  Your microphone needs a low voltage power source to create the charged field - this is the "mic power" you hear about.  You can get that mic power from a.) a battery box, b.) an external preamp that provides mic power, or c.) your MD if it provides mic power.  Usually these mics aren't overly fussy about the exact voltage (unlike some true "phantom power" mics), so someting in the range of 5-9v will probably work.  The better the mic quality, the more picky it will be about getting the exact right voltage.

Preamp

Ok, so you have a mic that is taking in sound energy and converting it into electrical energy, now what?  Well, the strength of the sound energy coming in is going to vary quite a bit.  A rock concert can go from near silent to earsplitting drums in a couple seconds, and the resulting electrical energy produced by the mics will also vary significantly.  This variation in energy is called the dynamic range of a mic, and is measured in decibels, which is a difficult scale of measurement to learn (or at least it was for me!).  The important thing is that the mic is going to be putting out a pretty wide range of energy due to the changes in sound volume.  

Now, as much energy as that mic may be putting out, it is still pretty low compared to what the electircal circuits in the MD need to work with.  So, some amplification is needed.  This is the job of the microphone preamp.  Now, the MD has an internal microphone preamp, but it has "fixed gain".  This means that the amount by which the preamp is going to increase the signal (the gain) is fixed, at some set amount.  For example, it might be designed to take the signal from the mic and amplify it by 20x (I have no idea about the actual amount of gain, this is just an example).  The Sony designers didn't build the preamp with you in mind - they probably had some basic low SPL recording in mind, like students recording class notes and the like.  So, when you get into a high SPL environment, your mics put out a strong signal, which the MD preamp then further amplifies, so the signal that goes to the rest of the MD is too strong and overloads the circuit, causing distortion/clipping.  Not good.

In a situation where all you have is the fixed gain from the MD, your only option to adjust the signal strength is to position the mics in the recording venue in such a way that the actual sound hitting the mics is at the right level.  This may be difficult or impossible to do, particularly if you're up front close to the PA speakers.

External Preamp

This is where the external preamp really shines.  Instead of having to move yourself around the room to get to a point that is quiet enough that you're not clipping the MD, you can increase or decrease the amount of gain until the strongest signal coming out of the mic is being amplified to just the right level for the MD - it is the strongest the MD can take, but won't overlaod it.  This allows you to do a couple things:  

1.) you can get right up near the speakers - this is important because the closer you are to the speakers, the more you're going to be recording the band's performance and not all the other crap noise going on around you (fans cheering, clapping, talking, airconditioner hum, outside traffic, etc.).  I think everyone on the board will agree good positioning of the mics can make a $500 rig sound better than a $5,000 rig.  

2.) You can use a "better" preamp.  The MD is not designed primarily for recording, so to save some bucks Sony puts in lower quality preamps.  That being said, Sony usually has pretty damn good preamps compared to their competition (the pre's in my D8 DAT deck are awesome).  However, Chris Church's preamps use better components and I would argue have better sound.  Much better.

3.) You can cover a larger dynamic range

This one's tricky.  I can explain using an example, but realize the actual numbers are meaningless, they're just to help with the example.  Let's say you're taping and you have sound levels of 3, 10, 15 and 20 coming out of your mics.  Let's also say your MD has fixed gain of 10x, and can handle a maximum signal of 100.  In that situation, you're going to overload your MD when you hit the 15 and 20 sound levels (150 and 200 respectively).  The combination of mics and preamp can only accept sounds from 0 to 10 (a low dynamic range).  Now, let's look what happens if you use an external pre and use the line-in selection (completely bypassing the preamp).  If you set the preamp to amplify 5x, then your output is 15, 30, 75 and 100 - you can record the entire dynamic range without clipping!  Now, the combination of mic, preamp and MD can handle a dynamic range of 0 to 20 - you've doubled the dynamic range.  Ultimately, you want to amplify the soft sounds (the 3's and 10's) as much as possible, but without overloading when you hit the 15's and 20's.  

Regarding getting the right recording level:

I saw somewhere else on TS that hand claps at about 1-2 feet are like 100 dB, which is about the max sound level you'll be able to stand at a show (and 100 db will hurt - ears start bleeding at like 110/120 db...).  You can adjust the preamp so that when you clap in front of the mics, it's just below the point of clipping, and as a rough setting you shoudl be good to go.  You'll have to play around with it to get it right.  One thing to keep in mind - if in doubt, run your levels low.  You may lose some of the softer sounds in the low end noise hiss, but you can always amplify the remainder in post-production using Audacity or the like.  If you clip, on the other hand, there's really no way to recover the recording.  You may be able to remove some of the distortion caused by the occassional clip, but if there's a lot of it your recording's probably junked.

Anyway, I hope that helps, and welcome to the hobby.  Get your checkbook out, it's gonna be a bumpy ride!!!  <grin>

Good luck!

Mike

[carbine000]

Thank you. This helped immensely.

I think my next problem is figuring out whether the recording is coming out clearly during the show or determining what or if anything needs to be adjusted.

[trustthex]

i as well thank you for that somewhat lengthy explanation.  +t

[carbine000]

Yes. +t.........if I can do it. LOL.

[dimm0k]

landshark: thank you for such a descriptive reply!  Because I'm waiting on the mic and preamp to arrive, I'm sort of flying blind of the stuff you've mentioned.  I do have a pretty good idea of it all, however I have one question on finding the right recording level with a minidisc player.  I take it the levels on the preamp are referred to as gain?  Well how do I go about finding out if a particular level of sound is going to clip at a particular gain?  Is this something that's going to be displayed on the minidisc or is it something I'm going to find out after the recording has been done?

[attheshow]

The minidisc has level meters. When you are in record+pause mode you can watch them. The to the right end of the meters you should see a spot marked 0db. If this lights up, you're levels are to high and you'll get clipping.